1. Field of the Invention
The present invention refers to an electric heating device for an automotive vehicle and a PTC heating element as such which is installed in said electric heating device.
2. Description of the Related Art
PTC elements have been widely accepted in electric heating devices for automotive vehicles, which is due to the self-regulating properties of PTC elements. Normally, a heat-generating element in an electric heating device consists of at least one PTC element and of strip conductors which are mounted at both sides in an electrically conducting, manner on the PTC element, and normally serve the electrical connection of the PTC element. Such heat-generating elements lie either directly or with interposition of an insulating layer against heat-emitting surfaces. The PTC elements are normally installed such that the PTC element delivers heat at both sides to heat-emitting surfaces.
Examples of electric heating devices with an insulation layer which covers at least one of the strip conductors on the outside are for instance given in EP 1 768 459 A1 and EP 2 637 475 A1, respectively.
EP 1 768 459 A1 discloses an electric heating device for heating air, in which the heat-emitting surfaces are formed by corrugated rib layers which adjoin the PTC element at both sides. In the already known prior art, plural PTC elements are accommodated in a positioning frame and contacted at both sides with contact sheets which form the generic strip conductors and serve the electrical connection of the PTC element.
An electric heating device which is also of the generic type is for instance known from EP 1 872 986 A1. In this prior art, heating ribs project into a circulation housing through which a fluid flows that is to be heated. The heating ribs form a U-shaped pocket which accommodates the PTC element as well as the strip conductors and insulation layers, which are respectively provided on the outside on the strip conductors. The PTC element and the strip conductors which are adjacent thereto at both sides for powering purposes are thereby accommodated in an electrically insulating manner in the heating rib. However, it is sometimes possible, for instance during operation of the electric heating device with the system voltage of an automotive vehicle of 12 V, to provide an insulation just at one side and to contact the PTC element directly with mass at the other side. “Mass” can here be formed by the outside of a heating rib or by a corrugated rib layer which at one side lies in a heat-conducting manner against the PTC element(s).
In the prior art known from EP 1 768 458 A, the insulation layer is formed by a two-layered structure which comprises a polyimide film and a ceramic layer. Especially in high-voltage applications and specifically in consideration of the operation of the electric heating device in an electric vehicle, attention must be paid to a safe electrical insulation of the PTC element and of the strip conductors contacting the element at both sides. A laminated insulation film for the same purposes is described in EP 2 109 345 A1.